3GPP Long Term Evolution, LTE, is the fourth-generation mobile communication technologies standard developed within the 3rd Generation Partnership Project, 3GPP, to improve the Universal Mobile Telecommunication System, UMTS, standard to cope with future requirements in terms of improved services such as higher data rates, improved efficiency, and lowered costs. The Universal Terrestrial Radio Access Network, UTRAN, is the radio access network of a UMTS and Evolved UTRAN, E-UTRAN, is the radio access network of an LTE system. In an UTRAN and an E-UTRAN, a User Equipment, UE, is wirelessly connected to a Radio Base Station, RBS, commonly referred to as a NodeB, NB, in UMTS, and as an evolved NodeB, eNodeB or eNodeB, in LTE. An RBS is a general term for a radio network node capable of transmitting radio signals to a UE and receiving signals transmitted by a UE.
It has been discussed during the work done on 3GPP Coverage Enhancements TR 36.824, v11.0.0 that there may be situations where an E-UTRAN UE is unable to access the network due to E-UTRAN Random Access Channel, RACH, coverage problems, i.e. the UE may have Broadcast Control Channel, BCCH, coverage and can measure on the cell and read its system information, but the network cannot receive any random access preamble attempts from the UE because the UE is power/coverage limited and hence the received signal in the network is thus too weak. Hence, the UE cannot connect to the E-UTRAN domain of the radio network.
A similar scenario as described above may occur, when the RACH coverage limitation of the first cell is caused by the fact that massive beam forming is required in order to provide users in the cell with coverage. This could be the situation if the first RAT is e.g. a future 5G cell operating in quite high frequency bands.
The “Mobile and Wireless Communications Enablers for the Twenty-twenty (2020) Information Society”, METIS, is a project co-founded by the European Commission and is a consortium of 29 partners. The project objective is to respond to societal challenges for the year 2020 and beyond by laying the foundation for the next generation of the mobile and wireless communications system. The frequencies being discussed for 5G in e.g. the METIS project, are much higher than what is commonly used for 3GPP accesses today—suggestions have been made for carrier frequencies >60 GHz.
In this frequency region, it will be almost impossible for network and UEs more than a few steps away from the network antenna to hear each other without the use of e.g. advanced multi-antenna techniques such as very directive beam forming. It will hence not be feasible to create a covering cell/sector which can be used for e.g. RACH purposes in this scenario.
Hence, there is a need for methods of enabling access to a network when a UE knows about a network, because it can e.g. measure on the cell and read its system information, but the network cannot receive any random access preamble attempts from the UE because the UE is e.g. power/coverage limited and hence the received signal in the network is thus too weak.